An axial flow gas turbine engine, such as an aircraft “jet-engine”, generally comprises an air inlet, a compressor section, a fuel combustion chamber, a turbine section, one or several rotatable drive shafts connecting corresponding compressors and turbines, an exhaust outlet and structures for supporting the drive shafts and for mounting the engine to, e.g., an aircraft.
The supporting structures are static parts that typically include an inner shell or ring, for connection to bearings and a centrally located drive shaft, and an outer shell or ring, for connection to, e.g., an engine casing, and where circumferentially distributed, load carrying airfoil shaped radial elements extend between and connect the inner and outer shells/rings. A primary axial gas flow through the engine thus flows through the areas formed between the rings and the radial elements.
The desire for low-weight components in air-craft applications has generated a need for supporting structures that are less heavy than the traditional casted structures but that still are capable of transferring radial loads, withstanding thermal load and an internal pressure, etc. Generally, such low-weight structures are manufactured by joining, typically by welding, a number of prefabricated parts together. The radial elements of such prefabricated structures usually consist of hollow airfoil shaped structural vanes. An example of a prefabricated supporting structure is shown in US 2007/140845.
A particular issue related to such prefabricated structures is the strength and durability of the joints, typically the welded joint formed when welding a first part of the vane butt to butt to a second part that forms an extension of the first part so that the welded cross-sectional connection becomes located somewhere along the radial length of the vane with the weld joint extending circumferentially around the radial element. A typical example is when the first vane part form part of a casted inner ring (hub) to which the remaining outer part of the vane and the outer ring are joined.
A supporting structure positioned in the turbine section of the gas turbine engine, such as a so-called Turbine Exhaust Case (TEC), is normally subjected to very high temperatures in the ring-strut-ring parts while being much cooler where connected to the bearing housing. This leads to a considerable thermal stress in the structure that, in combination with the considerable mechanical radial loads caused by flight manoeuvres, could limit the safe life of the welded joints, and thus of the entire component, due to thermal load driven crack propagation.
In order to increase the possibilities of making use of lighter, prefabricated supporting structures there is a desire for designs that reduce the effect of thermal stress on the life time of the component.